1. Field of the Invention
The present invention relates to a fuel feed apparatus and, in particular, a high pressure fuel feed connection to a fuel injector in an internal combustion engine to provide a conduit for leak-back fluid, a method for fitting such apparatus and an engine including said apparatus.
High pressure fuel injection systems used in, for example, diesel engines may be of the type in which the fuel is provided to the injectors from a "common rail" (a high pressure fuel manifold from which fuel for injection is taken off upon demand from the injector). In such systems it can be convenient, to limit engine height or for other reasons, to pass fuel from the rail via a pressure tube into a port in a side face rather than an upper face of the injector.
The upper part of an injector of the aforementioned type will often be enclosed within the body of the cylinder head but it may be necessary for it to be contained within an enclosure such as a camshaft housing above the cylinder head, particularly where the cylinder head is of shallow height in order to limit engine height and/or weight.
Several problems may arise in connecting a side feed to an injector in the above mentioned systems. In particular, fuel leaking from the vicinity of the injector connection may mix with and dilute engine lubricating oil carried within or above the cylinder head. This problem is exacerbated in that the leakage will normally be out of the sight of the engine operator.
Further problems arise with injectors of this type in that side forces may be imparted to the injector body which may cause deformation of the body and hence sticking of the injector moving parts. This situation can be particularly severe where the engine design does not readily permit the upper part of the injector to be directly supported by the cylinder head.
A further problem is the angular or lateral misalignment that can occur at the interface between the fuel feed conduit and the injector body. A rigid connection having limited means for correction of mis-alignment or tolerance build-up may lead to exacerbated fuel leakage at the interface and/or stress either at the connection or within the injector body.
2. Description of the Related Art
The problem in making a secure and leak-proof fuel feed connection to a side feed injector has been addressed in prior art. For example, U.S. Pat. No. 5,365,907 discloses a side feed connection to an injector in which arrangement a pressure tube is located in a recess in the cylinder head so that an inner end seats against a fuel inlet port in the injector and the tube is forced into firm engagement with the injector by a threaded tube-nut screwed into the cylinder head. The outer end of the tube extends through the tube-nut and is terminated in a means for securing a fuel supply pipe.
Patent application GB 2310891-A discloses a similar arrangement wherein a pressure tube having a frusto-conical collar is forced into engagement with the injector by a loose flange which bears on the collar and is retained to the cylinder head by threaded fasteners. Patent application JP 08-144886-A discloses a further arrangement in which a pressure tube passes through a passage in the cylinder head and into engagement with the injector and is terminated at an outer end by a flange. However none of the prior art discloses an injector side feed apparatus which would be suitable for fitment above, rather than within, the body of a cylinder head.
In cases where, for example, the space take within the cylinder head by the gas exchange mechanism leaves insufficient room for fitment of an injector side feed connection, or the cylinder head has only a shallow height, it may be convenient instead to make the connection above the cylinder head. In such cases, there would not be available the direct support of an upper part of the injector by the body of the cylinder head to resist the side forces which may be imparted by attachment of conventional side feed connections and this could result in bending of the injector.
In addition to a fuel feed, fuel leak-back provision is required with several common-rail injection systems because a portion of the fluid supplied is used in controlling the internal operation of and/or cooling of the injector and is then returned to the fuel feed system. It is otherwise known for fuel leak-back from an injector to be provided by direct communication between a relatively low leak-off port in an injector communicating with passages within a cylinder head but the long, small diameter, drillings in a cylinder head for this provision may be difficult to machine.
Patent DE 4427717-C1 teaches an apparatus capable of making a fuel feed connection to a side of an injector at a point above a main body of a cylinder head and due to the sliding nature of the connection side loading of the injector body can be minimised or avoided. However, there is no provision of appropriate means for fuel leak-back from the injector to a take-off point, and the leak-back path disclosed is of relatively high resistance, due to the presence of a threaded portion.